Most data processing systems require mass memory storage facilities that store large amounts of data. One such mass memory device is a hard file or hard disk. The hard file includes several surfaces that have a magnetic code for the magnetic storage of data. Data is stored and retrieved by the moving of a magnetic sensor or head over the surfaces. The surfaces are rotated at a high speed. Heads are located on top of each surface and are connected by an arm. Data is stored on the surfaces in concentric channels termed tracks Each set of tracks on different surfaces but with the same radius is called a cylinder. Each track includes a series of sequentially located sectors that are addressable for the storage and retrieval of data. When the heads are located on top of tracks of a specific cylinder, the arm does not move for reading or writing data from or to sectors on that cylinder. When information is located on a different track, the head will have to be relocated over that track to read or write data into sectors of that track. The movement of this arm is termed a seek operation.
As the speed of the data processing systems increases, so does the demand for a greater access speed. In some cases the speed of the rotating surface and the speed of the head in locating tracks can limit performance of the overall data processing system. This problem occurs when the access commands from the data processing system are not received fast enough to permit adjacent sectors to be accessed on the hard file surface in the same revolution. In other words, the head will have to wait for a second revolution for the next sector in the sequence to be accessed. If sequential sectors are being accessed from a specific surface and the arm is required to change cylinders because of an additional data request on another cylinder, the time to reposition the head over the new cylinder track to read the successive data block (seek time) increases the access time for data retrieval. Also the access time is increased by the rotational delay. Once the head is on the required cylinder the data transfer cannot start until the required sector is under the head.
It is an object of the present invention to provide an apparatus to decrease the access time for data from a rotating hard file.